This invention relates to tufting machines and more particularly to apparatus for adjusting and setting the gauge of the knife blocks of a cut pile tufting machine.
In the art of tufting cut pile or cut/loop fabric it is known to cooperatively engage a knife against a respective hook to sever all or selective loops on the hook. Conventionally, the knives are mounted in knife blocks which in turn are mounted in a knife bar. The conventional knife blocks have two or more elongated channels within which the knives are mounted and until recently such knife blocks had been mounted exclusively in a knife bar by means of a cylindrical spigot extending from the body of the block and which was inserted into a hole in a knife bar such as illustrated in U.S. Pat. No. 3,084,645. The angle of the block and thus the angle of the knives acting against the respective hooks was set by pivoting the block about the axis of the spigot and the block was secured by a screw or the like. As is known in the art the angle that the knife makes with the hook is a compound angle and is important for proper cutting of the arm on the hook as the knife and hook act in scissors-like fashion. The compound angle comprises an angle of inclination, i.e., the angle the block is pivoted about the axis of the spigot, and the angle of canter, this latter angle being provided by boring the spigot receiving hole in the bar at a slight angle.
Because of numerous cutting problems resulting from misalignment of the angle of inclination resulting from the inadvertant or incorrect setting of the knife blocks, especially when one considers the minimal space within which a mechanic must work, numerous attempts have been made to ensure that this angle is correctly set. One such proposal is illustrated in Lund U.S. Pat. No. 4,175,497 assigned to the common assignee as the present invention, in which pins on the knife bar engage slots on the knife blocks to position the blocks about the spigots. Moreover, especially in relation to fine gauge tufting machines, use has been made of knife modules within which the knives are fixably embedded by molding the knives into a body member having alignment surfaces which fix the compound angle of the knives. In that case the knives are aligned in a jig during formation of the module and each body member has alignment surfaces for clamping the module to the knife bar. However, a disadvantage of the modular construction is that when only a single knife is worn or broken, an entire module must be replaced. Although such a disadvantage may be insignificant for very fine gauge modules, it may be significant for other tufting machines.
Consequently, other proposals have been made, one such proposal being illustrated in Ingram U.S. patent application No. 524,150 filed Aug. 18, 1983 and assigned to Spencer Wright Industries, Inc. the assignee of the present invention. In that application knife mounting apparatus is disclosed including a knife mounting block for carrying a plurality of replacable knives in channels formed therein, and the block having reference surfaces for providing the correct angle of inclination and the correct angle of canter to the knives when mounted in the tufting machine. The reference surfaces cooperate with corresponding surfaces of the knife bar and simple clamping means secures the blocks to the knife bar. However, since these proposed knife blocks use no spigots the gauge between knives in adjacent blocks is not positively fixed. For example, in most tufting machines the gauge between adjacent needles in the needle bar sets what is known as "the gauging" that is, the gauge of the needle bar acts as a datum for the other gauge parts. Thus, after the needles are mounted in the tufting machine the hooks are inserted so as to cooperate with or suit the needles, and there may be spaces or gaps between secions of, for example, hook modules. Thereafter, the knife blocks are inserted to suit the hooks.
In practice, even though manufacturing tolerances may be very low, the length of a needle bar is approximately 160 inches which can result in a relatively substantial accumulated tolerance such as to result in off-gauge problems. When this occurs the hooks can be suited to the needles by setting short lengths of hook bars to the needles individually. Since knife blocks having no spigots do not have a spigot hole in the knife bar, there is no reference by which the gauge of the hooks can be matched for compensating for the accumulative tolerance of the needle bar. Thus, even though the individual knives may be matched or suited to the hooks and the needles, if a knife block is removed from the tufting machine there is no assurance that when reinserted therein the knives will be repositioned in matching disposition with the hooks. Rather than the gauge of the knives being constant, the knife blocks will abut adjacent blocks and the tolerance of the knife blocks will accumulate. Thus, some means of gauging knife blocks that have no spigots should be provided to permit repeatable positioning of all the knife blocks while able to compensate for manufacturing inaccuracies in the other components.